Identification of Listeria monocytogenes in retail deli environments

Investigator: Haley Oliver (Department of Food Science)

Project Report 2012 - 2013

Listeria monocytogenes is among the foodborne pathogens with the highest death toll in the United States. The current FDA-USDA quantitative risk assessment attributes the vast majority of human listeriosis cases to consumption of ready-to-eat (RTE) deli meats. An estimated 83% of listeriosis cases result from consumption of deli meats that are cross-contaminated at retail, yet very few studies have investigated L. monocytogenes transmission, prevalence, and persistence in retail delis. An ongoing longitudinal study in 30 retail delis in three states found L. monocytogenes prevalence in many of the delis, even after sanitation. To better understand L. monocytogenes persistence in delis, ARS-funded researchers at Purdue University's Center for Food Safety Engineering in West Lafayette, Indiana, used Pulsed Field Gel Electrophoresis (PFGE) DNA fingerprinting to determine if the same L. monocytogenes strain was being recovered routinely from a deli (evidence of persistence) or if L. monocytogenes was transient in the deli environment. The PFGE typing of over 800 L. monocytogenes isolates from retail delis found significant similarities in the DNA fingerprint patterns and led to the conclusion that over 40% of the delis studied had evidence of persistent L. monocytogenes contamination. The substantial genetic similarity between the isolates suggests that a small number of highly related L. monocytogenes types are responsible for retail deli contamination. This study concludes that: (i) some retail delis have an increased likelihood of prevalent and persistent L. monocytogenes contamination, (ii) there is a need to develop feasible and practical approaches to control L. monocytogenes in these environments, and (iii) control of L. monocytogenes in retail delis will likely lead to an decrease in listeriosis cases in the United States.

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